Two-way radio communication



Nov. 28, 1944. 5. w. GILMAN 2,363,533

TWO-WAY RADIO COMMUNICATION Filed Dec. 16, 1942 AHA VVVI

INVENTOR G. W G/LMAN fa zw ATTORNEY Patented Nov. 28, 1944 TWO- WAY RADIO COMMUNICATION George W. Gilman, Short Hills, N. .I., ass'ignor to Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application December 16', 1942, Serial No. 469,167

9 Claims.

The present invention relates to radio telegraphy or telephony and especially tomeans for rapidly monitoring an ether wave band and setting upa communication channel on a wavelength in that band.

An object of the invention is to facilitate finding and putting to use a suitable wave-length for communication purposes especially at the times when many of the available wave-lengths in the ether 'wave band of interest are already in use.

A feature of the invention comprises a means for simultaneously scanning an ether wave band and tuning a radio transmitter or receiver or both.

A further feature comprises a means for signaling the distant radio station through the scanning or monitoring set of that station.

The present invention, in its more specific aspects, may make use of a visual ether wave band monitoring apparatus, in itself known in the art, such as a cathode ray oscilloscope to indicate on a frequency scale the points corresponding to the wave-lengths that are in use at a given time. In accordance with a feature of the invention, an ether wave band monitoring circuit is coordinated with radio station tuning means to facilitate rapid selection and appropriation of an available frequency. As soon as a frequency is selected and appropriated by the transmission of a carrier wave of the selectedfrequency, other radio stations having similar equipment receive a busy indication showing that such frequency has been taken for use, this indication appearing as a line, spot or other signal on the monitoring oscilloscope of each such station. The wanted station is then called, as for example, by flashing the call signal of that station on the monitoring oscilloscope; and, in accordance with a feature of the invention, the operator at the called station upon noting the call signal can quickly place the station in twoway communication with the calling station by merely moving the station tuning control so that an index on the oscilloscope coincides with the flashing line orspot. There is no necessity of reading a position on a scale and translating the reading into a tuning adjustment since the station tuning control is coordinated with the ether wave, band monitoring circuit.

Thenature of the invention and its objects and features will appear more fully from the following' detailed description in connection with the accompanying drawing.

In the drawing, Figs. 1 and 2 are block schematic diagrams of two radio stations adapted for communication with each other and embodying the present invention;

Fig. '3 is a frequency diagram to facilitate the description of the general method of operation according to the invention; and

Fig. 4 is a circuit diagram of the scanning or monitoring and tuning circuits such as. may be employed. in the stations in Figs. 1 and 2.

Referring first to Fig. 1, a radio transmitter it! is indicated as having a telegraph input circuit l2 and a telephone input circuit l3. Similarly, radio. receiver H is indicated as having a telegraph output; circuit l4 and telephone output circuit l5. The. showing of these parts is purely conventional and merely for illustrative purposes; and it is. assumed that any suitable known types of apparatus may be used for these parts. ample, may comprise suitable power amplifying and antenna coupling circuits and the telephone input l3 may comprise suitable circuits for modulating the radio wave by input speech waves from subset l6. Carrier waves are supplied to the telegraph input i2 and telephone input 13 from a source H over lead l8.

The radio receiver H may comprise an antenna coupling circuit and superheterodyne stage, the superheterodyning frequency being furnished from modulator l9 over lead 20. An oscillator 2| delivering to the modulator 1-9 a wave of the intermediate frequency used in the radio receiver H is combined with the carrier wave furnished by lead l8 to supply a heterodyning wave of proper frequency. For example, if the carrier wave used for both transmitting-and receiving has a frequency of 2,000 kilocycles and if an intermediate frequency of kilocycles is used in the receiver H, the source it delivers a wave of 100 kilocycles and circuit 201' then applies to the receiver H a wave having a frequency of 2,100 kilocycles, which upon beating with the received carrier wave yields an intermediate frequency of 100 kilocycles for selection and detection by radio receiver ll. Ganged switches 23 permit connection of the desiredtransmitting and receiving circuits to the radio transmitter 30 and receiver Ill. I

Thesubscri'oers set It is shown connected to the telephone transmitting and telephone receiving circuits l3 and I5 by way of hybrid coil 24 providedwith balancing network 25-. Alterna tively, a transmit-receive switch may be used in accordance with known practice controlled, for example, from a push button in the subscribers set IS.

The ganged switches 22, 23 havethree positions: As shown, the upper position is for monitoring, the middle position is for telegraphy, and the lower position is tortelephony. The normal position is the upper or monitoring position.

ljhe radio transmitter Ill, by way of GX' When switch 23 is in monitoring position, the radio receiver II is connected to the monitoring circuit indicated generally by the box 26 and the oscilloscope 21. The carrier generator I! is provided with a manual tuning adjustment 28 and also with a sweep circuit (to be described) in the box 26 for sweeping the carrier frequency over as wide a wave band as is to be scanned at any one time, this band being sufliciently wide to include the frequencies of a number of communication channels in an ether wave band. By means of circuits to be specifically described hereinafter, whenever the frequency of the oscillator H in its sweep allows receiver II to pick up a carrier wave in use, the corresponding indication appears in the form of a line or spot on the oscilloscope 21. Certain of these marks are indicated in the drawing at a, b, and 0. An index mark 3| shows the relative location on the circular sweep scale 32 of the mean frequency of the oscillator By observing the markings on the oscilloscope screen, the operator is enabled to tell which portions of the ether wave band that is being scanned are in use and which are free. Assuming that the space between marks a and b is free end that the operator desires to utilize this part of the band for communicating purposes, he moves the dial 28 to shift the frequency of the source so that index 3| falls in the space between the marks a and b. In reality the index 3| remains stationary, while the marks, a b, 0, etc., rotate as the dial 28 is turned. When the operator has tuned the oscillator H to the desired frequency as indicated on the oscilloscope, he moves the ganged switches 22 and 23 out of the monitoring position into the middle position, thereby connecting the telegraph input and output circuits l2 and M to the transmitter l and receiver II, respectively. Movement of a third switch arm 53 (Fig. 4) out of its monitoring position stops the sweeping action of the oscillator I! and leaves the frequency set in accordance with the positioning of the dial 28, in a manner to be described in connection with Fig. 4. This causes the carrier wave from the oscillator H to be transmitted continuously from the transmitter l0 except as it may be interrupted or modulated by the telegraph input circuit l2.

The equipment at the station shown in Fig. 2 and at other idle associated stations is identical with that in Fig. 1 and the parts are indicated by the same reference characters primed. When the foregoing operations have taken place, therefore, and with ganged switches 22 and 23 in monitoring position, an additional line or spot appears on the oscilloscope 21', between the lines a and b, since receiver detects the carrier waves sent out from oscillator IT. The operators at the station in Fig. 2 and other idle associated stations, upon observing this line or spot, do not as yet know which station is being called. Assuming, however, that the station in Fig. 2 is to be called from the station in Fig. 1, the operator at the latter station actuates telegraph input circuit-l2 to interrupt the transmitted carrier wave in accordance with the telegraph code of the call letters of the station in Fig. 2 so that the line or spot on the oscilloscope 21' resulting from the carrier wave from oscillator I! in Fig. 1 flashes in accordance with the code of these call letters. The operator at the station in Fig. 2, upon noting his coded call letters, turns the dial 28' until the index 3| exactly coincides with the flashing line or spot,

whereupon he moves the ganged switches 22', 23' to their middle position. Movement of a third switch arm 53 out of its monitoring position stops the sweeping action of the oscillator I1 and leaves the oscillator set at the same frequency as oscillator I! of the calling station in Fig. l. The operator at the station in Fig. 2 may then actuate his telegraph input circuit l2 to communicate with the station in Fig. 1; and both stations are now in condition to communicate with each other either by telegraph or by telephone, depending upon the position of the ganged switches.

It is thus seen that tuning at the oscillator I! is coordinated with the indications on the oscilloscope 21 so that the operator is relieved from taking any actual numerical readings or translating readings on the oscilloscope into settings on the dial 28. The entire operation is reduced to relative positioning of lines or spots on the oscillopscope with reference to the index 3|.

The indications on the oscilloscope 21 represent frequencies spaced above and below some mid-band or mean frequency. This is indicated in Fig. 3 where the scale is shown as a straight line instead of a circle, for convenience. Several mean-frequency settings are indicated at F0, F1 Fe. These mean frequencies are determined by the manual adjusting means 28. Concentrating attention for the moment on mean frequency F3, the heavy horizontal line indicates that the sweep with this mean-frequency adjustment extends between about F0 and about F's as limitedby the visible portion of the oscilloscope 21. Markings corresponding to intercepted waves are shown at a, b, 0, etc. If the wavelength corresponding to frequency F2 is to be selected for use, the dial 28 is moved to bring the index 3| at the top into a position between marks I) and 0, these being indicated in the diagram of Fig. 3 on the horizontal line :r. With this manual adjustment, the sweep now extends between an upper frequency in the neighborhood of F5 and a lower frequency somewhat below F0. From one point of view, diagonal line 1/ in the diagram represents the position of the index 3|; and the several horizontal lines show how the markings a, b, 0, etc. are shifted with respect to the index 3| as the manual adjustment of the oscillator is shifted.

Referring to Fig. 4, the source I! is shown as a vacuum tube oscillator of conventional design having a resonant frequency determining circuit including as elements the tuning condensers 60 which are adjustable by the knob 28 to change the frequency. The circuit l8 of the output carrier wave is coupled to the resonant circuit inductance 6|.

For the purpose of providing a sweep, a reactance control tube 5i] is provided for changing the frequency of the oscillator H as a function of the voltage impressed on the control grid of the tube 50. For this purpose, the plate circuit of the tube 50 is connected across the inductance 6| while the control grid is coupled to the oscillator circuit through a phase shifting circuit comprising resistance 62 and capacity 63 in a manner known in the art. When relatively low frequency voltages are applied to the control grid of tube 59, corresponding changes are made in the oscillator frequency.

A sine wave sweep generator 5| of conventional design is provided for supplying to transformer 54 a sweep controlling frequency of, for example,

25 or" 501 cycles per second or any others'uitable frequency. One Winding of this transformer is included in the control grid circuit of tube 50 sothat the frequency of the oscillator I1 is caused to vary'up and down from its mean-frequency setting as indicated in Fig. 3.

The oscilloscope 21 is shown as having vertical and horizontal plates connected to the output of amplifier tube 52 through the medium of phase shifting circuits 55, 56' and 51, 58 to provide a rotating field for the oscilloscope beam when a sine wave of suitable frequency is applied to the grid of amplifier 52. Such a sine wave is applied through a third winding on the transformer 54 from the sweep generator The beam is, therefore, caused to rotate and trace a circular path 32' on the screen. The grid circuit of the amplifier 52 is shown connected through one arm of switch 23 in the monitoring position to the conductor 64 leading from radio receiver H in i Fig. 1. When the frequency of the oscillator I1 is. cyclically swept through its monitoring range, the receiver II has its tuning swept over the desired ether wave band; and, whenever wave energy is intercepted, it is applied from conductor 64 over switch 23 to the grid of amplifier 52 and appears as an impulse which is applied to both the vertical and horizontal plates of the oscilloscope with the result that a radial deflection of the oscilloscope beam occurs and produces such a line or spot as a, b, or c, at a point along the path 32 indicative of the frequency of the int'ercepted wave.

Since the control tube 50 and the oscilloscope driving tube 52 are both coupled to the sweep generator 5|, the readings on the oscilloscope are coordinated with the instantaneous frequency of the oscillator H. In order to adjust the operating wave-length of the station in Fig. 1 to correspond with any part of the frequency scale of the oscilloscope, it is, therefore, only necessary to move the knob 28 until the mean frequency given by theindex 3| coincides with the desired indication of instantaneous frequency given by the radial deflections a, b, etc. or by space between them.

When the desired adjustment has been made, switch 23 is moved clockwise in Fig. 4 to either the middle or lower position, depending upon Whether telegraph or telephone communication is desired. Upon movement of the switch 23 out of its monitoring position, the plate circuit of the sweep generator 5| is broken by means of switch 53 ganged to switch 23; and connection from the radio receiver to the input of amplifier 52 is broken at switch 23. In this way, the operation of the sweep generator 5| is stopped, leaving the oscillator transmitter l0 and receiver tuned to a frequency corresponding to the setting of the knob 28; and the oscilloscope 21 is disconnected from the receiving circuit.

What is claimed is:

1. A two-way radio station comprising a radio transmitter and a radio receiver, means to supply a radio wave of adjustable frequency to said transmitter and a radio wave of adjustable frequency to said receiver to enable two-way communication on one of a plurality of channels, means for monitoring an ether wave band to indicate available frequencies, means to coordinate the monitoring means with the radio wave supply means to facilitate adjustment of the radio waves supplied to the transmitter and receiver' to: correspond with the indications on the monitoring means, and means to disable the monitoring means and appropriate a selected communication channel.

2. A two-way radio station comprising a radio transmitter and a radio receiver, means to supply a radio wave of adjustable frequency to said transmitter for transmitting purposes and a radio wave of adjustable frequency to said receiver for enabling reception of selected radio communication waves, means connected to the receiver and to the means for supplying adjustable frequency waves to both the transmitter and receiver for monitoring an ether wave band to indicate wave frequencies in use, means to prevent transmission from said transmitter during monitoring, means to adjust the frequency of the radio waves supplied to said transmitter and receiver in accordance with the indications on said monitoring means, and means operable after completion of the adjustment for disabling both said monitoring means and said means for preventing transmission whereby said station is conditioned for transmitting and receiving at the adjusted frequency of said supply means.

3. A two-way radio station comprising a radio transmitter and a radio receiver, an oscillator for supplying a radio Wave to said transmitter and a heterodyning Wave to said receiver, a reactance control tube for said oscillator, an oscilloscope, a sweep generator coupled to both said reactance control tube and said oscilloscope, a switch having a monitoring position and one or more communicating positions, said switch in its monitoring position disabling said transmitter and connecting said radio receiver to said oscilloscope, means for manually adjusting the frequency of said oscillator to vary the mean frequency of the monitoring band, said switch in any other than its monitoring position disabling said sweep generator to permit the oscillator frequency to remain at the frequency set by said manual control and rendering said transmitter operative.

4. In a two-way radio communicating system, a transmitting station and a distantly located receiving station, means at the transmitting station to monitor an ether wave band to determine an energy-free region, means to appropriate a radio wave frequency in such region by sending out a wave of the appropriated frequency, means to interrupt said wave to call the distant station, means at the latter station to monitor the same ether wave band, an oscillator at said latter station for generating transmitting carrier waves and receiving heterodyne waves, means to tune said oscillator, means coordinating said monitoring means at said receiving station with the tuning of said oscillator to facilitate manual adjustment of the oscillator frequency to frequencies indicated on the monitoring means, means causing said monitoring means to pick up the inter rupted waves from said transmitting station and indicate the frequency thereof.

5. In a two-Way radio communicating system, a local calling radio station and one or more distant radio stations of which one is to be called, means at th local stationto monitor an ether wave band to determine an energy-free region, an oscillator for generating a transmitting carrier wave, means to appropriate 2; radio wave frequency in such region by transmitting a carrier Wave of the appropriated frequency to give an indication at each distant station, means to transmit code signal by said wave to call a particular distant station, means at each distant station to monitor the same ether wave band, an oscillator at each distant station for generating a carrier wave for the transmitter and a heterodyne wave for the receiver, means to tune said oscillator, means coordinating said monitoring means at each distant station with the tuning of said oscillator to facilitate manual adjustment of the oscillator frequency to a selected frequency indicated on the monitoring means, means causing said monitoring means to pick up the coded waves from said local station and indicate the frequency thereof.

6. A two-way radio station comprising. a. radio transmitter and a radio receiver, a switch having a first, second and subsequent positions, a wave band monitoring oscilloscope, a radio Wave oscillator of adjustable frequency coordinated with said oscilloscope to have instantaneous frequencies definitely related to each monitored wave frequency, said switch in its first position disabling said radio transmitter and connecting said wave band monitoring means to said radio receiver to receive ether wave energies, said switch in its second or a subsequent; position enabling said transmitter to transmit radio waves generated in said oscillator and disabling said monitoring means.

7. A two-way radio station comprising a radio transmitter and a radio receiver, a tunable oscillator feeding a transmitting carrier wave to the transmitter and a heterodyne wave to the receiver, an oscilloscope, a sweep generator coupled to said oscilloscope and to said tunable oscillator to vary the frequency thereof in cyclical manner about a mean frequency, a switch normally connecting said oscilloscope to said receiver to cause scanning of an ether wave band, said switch normally disabling said transmitter,said oscilloscope while scanning also indicating coded call signals received over a channel of particular frequency, manually operated tuning means to adjust the frequency of said oscillator to correspond with said particular frequency, and means controlled by said switch for enabling said transmitter to transmit and for stopping the cyclic variations in frequency of said oscillator.

8. In combination a radio receiver, a normally inactive radio transmitter, means for simultaneously controlling the frequency to be radiated by said transmitter and the frequency to which said receiver is responsive, cyclically varying means for causing said transmitter and receiver frequencies to sweep over a range of frequencies, means for monitoring the output of said receiver to indicate the frequencies in use within said range of frequencies, and means for interrupting the sweeping action and rendering said transmitter active at a selected frequency in said frequency range.

9. The method of establishing two-way communication between two radio stations comprising producing visual indications at both stations of the frequencies in an ether wave band that are in use, selecting at the calling station a carrier frequency that is not in use and tuning the calling station transmitter to emit a wave of the selected frequency, interrupting said emitted wave in accordance with a code signal indicative of the called station whereby a visual indication is given at the called station of both the called station and the frequency of the selected Wave, and adjusting the called station carrier frequency to the indicated value.

GEORGE W. GILMAN. 

